A. Field of the Invention
This invention relates to the reinforcement of castable compositions such as concrete or mortar mixtures by fibers having a plurality of different aspect ratios and lengths for improving the mixing of the different size fibers without clumping and improving the toughness of the composition.
B. Description of the Related Art
Steel fibers and synthetic fibers have been added to concrete and mortar for inhibiting the start of cracking and for inhibiting crack propagation and retarding crack widths. Fibers of uniform length have also been added to concrete and mortar for increasing the toughness of the composition for large deflections after the start of cracking. However there has been no combination of different metal fiber aspect ratios to improve the toughness of compositions at small deflections particularly after cracking has started with shorter length fibers while still improving the toughness of the concrete or mortar with longer fibers.
A problem with adding fibers to a concrete or mortar mixture is balling where the fibers of one length will ball together and they thereafter cannot be easily separated. They become entangled and cannot be separated. The mixing of fibers of different lengths in desired proportions then becomes even more difficult as the fibers of different lengths when shipped separately clump together and can't be separated. Mixing of the fibers in the concrete or mortar will compact the entangled fibers making the balling worse.
Some attempts to add fibers of higher aspect ratios without balling used fibers of the same size glued together at the edges with water-soluble glue. Gluing the fibers together in effect presented a lower aspect ratio fiber for easier mixing. When mixed with concrete the fibers got separated without a balling problem. However, only one size fiber was added to the mixture by this method.
Various mixing sequences and techniques have been developed to mix fibers of one size into concrete to avoid balling. However the sequences are highly labor intensive or involve additional equipment, or additional mixing time to try to avoid balling. This adds to the costs and if not properly performed balling still occurs.
It is desired to be able to select a mixture of the specified lengths of fibers and to mix them into concrete or mortar without clumping or balling to provide a homogeneous mixture resulting in the desired toughness for the end product.